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=============================================================================
FreeBSD-EN-14:07.pmap                                           Errata Notice
                                                          The FreeBSD Project

Topic:          Bug with PCID implementation

Category:       core
Module:         kernel
Announced:      2014-06-24
Credits:        Henrik Gulbrandsen
Affects:        FreeBSD 10.0-RELEASE
Corrected:      2014-03-04 21:51:09 UTC (stable/10, 10.0-STABLE)
                2014-06-24 19:05:08 UTC (releng/10.0, 10.0-RELEASE-p6)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:http://security.freebsd.org/>.

I.   Background

Process-context identifiers (PCIDs) are a facility in modern x86
processors, which tags TLB entries with the Id of the address space
and allows to avoid TLB invalidation on the context switch.

II.  Problem Description

Due to bug in the handling of the mask of the CPU set where the given
address space could have cached TLB entries, stale mappings could be
seen by multithreaded programs.

III. Impact

Applications, most notably Java, which makes heavy use of threads may
randomly crash due to the inconcistency.

IV.  Workaround

Systems that do not run have a CPU that supports the Process-Context
Identifiers feature are not affected.

The system administrator can add the following to /boot/loader.conf
which disables Process-Context Identifiers to workaround this problem:

	vm.pmap.pcid_enabled="0"

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

2) To update your present system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 10.0]
# fetch http://security.FreeBSD.org/patches/EN-14:07/pmap.patch
# fetch http://security.FreeBSD.org/patches/EN-14:07/pmap.patch.asc
# gpg --verify pmap.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r262753
releng/10.0/                                                      r267829
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

The latest revision of this Errata Notice is available at
http://security.FreeBSD.org/advisories/FreeBSD-EN-14:07.pmap.asc

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